This invention relates to an iron golf club, and, more particularly, to an iron in which the club head is provided with a slot behind the striking face of the club head to provide a flexible and resilient plate for striking the ball.
When a golf iron is swung and the head of the iron impacts a golf ball, the club head absorbs energy. If the energy which is absorbed by the club during impact is not transferred to the ball before the ball leaves the club, this energy is lost with respect to the objective of propelling the golf ball. The duration of the impact between the ball and the club head, i.e., the time that the ball stays in contact with the club head, is extremely short, usually of the order of 1/2 millisecond, and all golf irons lose some energy which is not transferred to the ball within this time. This lost energy can take the form of shock waves, for example, which remain in the club after the ball leaves the face of the club.
If the amount of energy which is stored in the club when the ball leaves the club can be reduced, more energy will be transferred to the ball, the ball will leave the club with greater velocity, and the ball will be propelled farther. Attempts have been made to provide golf clubs with resilient faces for increasing the energy which is transferred to the ball. For example, British Pat. No. 379,032 describes a golf club in which a resilient metal plate is mounted on the club head with a cavity behind the plate. U.S. Pat. No. 1,854,548 describes making the striking face of a golf club more resilient by removing metal from behind the striking surface. U.S. Pat. No. 3,061,310 describes a club with a resilient ball-engaging wall which is spaced from the main body of the club head by a slot, but this club is a putter and is not intended to withstand the impact forces which are encountered by a striking iron. In recent years investment cast irons have become popular in which the thickness of the head is greater around the periphery of the striking face than in the center of the face.
While improvements in golf club head design have resulted in some increase in distance, energy still remains in the club after impact and is therefore lost. This can be best appreciated by considering the forces involved when a golf club strikes a golf ball. A golfer who would be considered a long hitter might develop a club head speed of about 137 feet per second with a 5 iron. The force exerted by the ball on the face of the club at that speed will be of the order of 1300 pounds. The magnitude of the impact force and the extremely short duration of impact necessarily means that some energy will remain in the club when the ball leaves.